128 Mr Herschel on a Remarkable Occurrence of Serpentine 



is so encumbered with blocks of the sienite rolled down from 

 above, that the actual union of the two rocks cannot be seen 

 except on Canzocoli. The specimens, (1) and (2) however, 

 were detached from a point of contact, where the dolomite, at 

 least, is undoubtedly in situ, and presents no peculiarity of ap- 

 pearance, but that of being less saccharine, and more scaly in 

 its structure than the usual dolomite of the country. 



On Canzocoli, however, the case is different. The actual 

 junction of the rocks is there accessible, and had fortunately 

 been in some degree laid bare by some travellers who had vi- 

 sited it the day before,* and who pointed out to me the locali- 

 ty. The phenomena of this junction are very remarkable. 

 The dolomite distinctly underlies, at an angle from 50° to 60°, 

 dipping towards Predazzo, and appears to have, sustained a re- 

 markable alteration in its mineralogical character, presenting, 

 in place of its usual highly crystallized saccharine structure, a 

 flaky and very talcose appearance, arising from the interposi- 

 tion of infinitely thin pearly plates, which give it a tendency to 

 break in irregular wedge-formed masses, and impart to it a 

 smooth feel, in some degree steatitic. (Spec. 12.) The incum- 

 bent sienite is no less affected. Its grain is smaller, and it is in- 

 tersected by innumerable veins parallel to the plane of junc- 

 tion, of a white mealy substance, which partly dissolves with 

 effervescence, and partly gelatinizes with nitric acid. (Spec. 

 13.) Chabasie in regular small crystals also occurs in the fis- 

 sures of the sienite, (spec. 6, 7,) and a beautiful small dode- 

 caedral garnet was found among a quantity of the white mat- 

 ter (13) on subsequent examination. (Spec. 14>.) 



But the most remarkable fact attending this junction, is 

 the occurrence of a thin lamina of serpentine between the 

 sienite and the dolomite. When I first encountered it, on 

 prosecuting further the excavation commenced by the gentle- 

 men above alluded to, I had no suspicion of its nature, its ap- 

 pearance being dark and dull from the moisture which had 

 penetrated it, and from a degree of weathering it had un- 

 dergone. The same causes had rendered it much more friable 

 than is usual with this rock, so that, being quite in doubt as to 

 its nature, I contented myself with merely packing up the 



• II Marchese Petrucci, di Pezaro, Mons. Bertrand Islin, and Signior 

 Perolini, di Bassano. 



